Plotting multiple straight lines using random number loop

Question

Stuart 2012-4-16

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编辑： Walter Roberson 2016-6-17

Hi,

I'm trying to plot several lines of different gradient from the same point on a graph. The gradient is determined by the angle phi, which has a mean angle of 45 degrees and a standard deviation of 3.

Considering the equation of a straight line y=mx+c, c is determined by the gradient and coordinate the line passes through.

I am having a problem with getting multiple plots and I'm not sure why. Currently the plot is only a single line.

My code is:

n=100;
x0=3;
y0=4;
x=linspace(0,20,n);
for i=1:n;
  phi(i)=45+3*randn;
  m(i)=tand(phi(i));
  c(i)= y0-m(i)*x0;
end
y=m(i)*x+c(i);
plot(x,y)

Can someone please help me find a solution for this problem?

Thanks.

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Stuart 2012-4-16

Yes it is. I thought I'd present the basic problem rather than all the malarky that came with it!

I apologise if its agaisnt the boards rules / etiquette, it was driving me mad and needed help!

Anshuman Tiwari 2015-6-8

编辑：Walter Roberson 2016-6-17

在 MATLAB Online 中打开

Stuart Try This :

n=100;
x0=3;
y0=4;
x=linspace(0,20,n);
for i=1:n;
  phi(i)=45+3*randn;
  m(i)=tand(phi(i));
  c(i)= y0-m(i)*x0;
  y=m(i)*x+c(i);
  hold on 
plot(x,y)
hold off 
end

This will work

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Answer 1

Thomas 2012-4-16

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I guess this is what you want..

n=100;
x0=3;
y0=4;
x=linspace(0,20,n);
y=[];
for i=1:n;
  phi(i)=45+3*randn;
  m(i)=tand(phi(i));
  c(i)= y0-m(i)*x0;
y(i,:)=m(i)*x+c(i);
plot(x,y(i,:))
hold on
end

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Stuart 2012-4-16

You've nailed it!

Yes! Cheers for that!

Stuart 2012-4-16

Hi Thomas,

Thanks for your help.

After modifying the code slightly it has stopped working. Can you see why?

(Answer has been posted below as another answer)

Your help is much appreciated.

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Answer 2

Stuart 2012-4-16

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Hi, I've slightly modified the code you've helped me with and now it doesn't seem to work. x seems to be changing from what I specified and so the plot only works to a certain x value.

The new code is:

%Finding the maximum and minimum points of entering the hoop
%Initial launch data
x0=20;
y0=4;
n=50;
x=linspace(0,27,n);
y=[];
mean_phi=atand((7.5-y0)/(26.425-x0));
sd_phi=1;
for i=1:n;
%Find the mean angle phi and then actual phi.
    phi(i)=mean_phi+sd_phi*randn;
    m(i)=tand(phi(i));
    c(i)= y0-m(i)*x0;
    y(i,:)=m(i)*x+c(i);
    plot(x,y(i,:))
    hold on
    axis equal
    Courtlay
    hring2= rectangle('position',[26.324 7.399 0.202 0.202], 'curvature',[1,1],'EdgeColor',[0 0 0],'LineWidth',0.02);
end

What have I done wrong?

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Thomas 2012-4-16

You do not have to call it and the rectangle code in the for loop.

You can call it outside..

Stuart 2012-4-16

Once again, you've nailed it.

Thank you again.

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Answer 3

Gaspar Cid 2016-6-17

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编辑：Gaspar Cid 2016-6-17

Hey there guys,

Sorry to bring back this question, but i'm trying to plot multiple RADIAL straight lines from x0 and y0 and i can't do it (not random radial lines, the idea is that they fill a circle), how should i modify this code to make this happen? I guess that must be some change in phi...

I would really appreciate some help,

Thanks

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Answer 4

Gaspar Cid 2016-6-17

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Well, i finally did this

N=20000
n=100;
x0=3774;
y0=-352;
x=linspace(-N,N,n);
y=[];
for i=1:n;
phi(i)=(360./n).*i;
m(i)=tand(phi(i));
c(i)= y0-m(i)*x0;
y(i,:)=m(i)*x+c(i);
plot(x,y(i,:))
hold on
end